We performed cytogenetic analyses using banding techniques on 89 adults with acute nonlymphoblastic leukemia prior to receiving protocol chemotherapy. The relationships of cytogenetic findings both to outcome and to other pretreatment variables (particularly the presence or absence of Auer rods) were analyzed. Patients were followed up to 90+ months. When patients were grouped according to cytogenetic findings (NN: all normal metaphases; AA: all abnormal metaphases; AN: both normal and abnormal metaphases; F: no evaluable metaphases; I: insufficient (less than three) metaphases) no significant differences were noted with regard to age, sex, terminal transferase positivity, complete remission rate, remission duration or survival. The marrow aspirates of patients with only normal (69%) metaphases or no evaluable metaphases (64%) were more likely to display Auer rods than specimens from individuals with only abnormal (26%) or a mixture of normal and abnormal (42%) metaphases (p = 0.03). The presence of Auer rods in the pretreatment marrow aspirate was associated with an increased complete remission rate (71% vs 41%, p = 0.004), median remission duration (12 months vs 9 months, p = 0.02), and median survival (13 months vs 4 months, p = 0.01). Using multivariable analyses, the presence or absence of Auer rods was the pretreatment factor that most significantly predicted response and survival in this group of patients. The presence of a normal karyotype in the initial cytogenetic preparation is associated with the presence of Auer rods. The finding of Auer rods in the initial bone marrow predicts greater response and longer survival in acute nonlymphoblastic leukemia.